Bacterial blight—Pseudomonas syringae
Bacterial blight damage varies depending on the host plant and strain of Pseudomonas syringae
involved. On some species, such as California bay and English laurel, injury is normally confined to leaves,
causing a leaf blight. Leaf blights cause small black angular spots; large, irregular, brown spots form
on leaves. Blossom and tip dieback, vein blackening, leaf spots, or stem cankers are common symptoms on
oleander, pine, and poplar. On flowering fruit trees, brown to black lesions on the flowers, fruits, and
stems form; branch cankers and brown streaks in the wood may also occur. On other hosts, elongated lesions
may appear on twigs and infected tissue may ooze during wet weather. Trees may have gum deposits. Bacterial blight is promoted by prolonged
rainy springs. Symptoms may be more extensive in wetter areas.
Identification | Life
Prune branches showing dieback and severe blight. Space plants
to provide good air circulation. Prune
during the dry season when infection is less likely to occur.
Do not wet foliage with overhead irrigation; do not overfertilize.
Small plants can be protected to some degree by keeping them
covered by plastic
(or moved under plastic). Plant resistant
species if available. If the
disease is systemic or cankers appear on the trunk, the tree
will probably die and should be removed. If the disease is
confined to leaves, damage is not usually serious and trees
normally recover. Sprays do not give reliable control.
Pseudomonas sp. on lilac
Gumming on almond branch
Apple blossoms and shoots killed by blight